In the past, twisted pair cables were utilized in applications where data speeds reached an upper limit of about 20 kilobits per second. Recent advances in wire technology and hardware equipment have pushed the upper limit of twisted pair cable applications to about several hundred megabits per second.
Twisted pair technology advances have primarily focused on near end crosstalk. Both U.S. Pat. No. 3,102,160 and U.S. Pat. No. 4,873,393 teach the importance of utilizing pairs which are twisted with lengths of lay different from integral multiples of the lengths of lay of other paired conductors within the cable. This is done to minimize electrical coupling between paired conductors.
U.S. Pat. No. 5,015,800 focuses on another important issue of maintaining a controlled impedance throughout the transmission line. It teaches how impedance can be stabilized by the elimination of air gaps around a twisted pair embodiment through the use of a dual dielectric which has outer layers bonded after the insulated conductors are twisted.
When two or more pairs of different average impedance are connected together to form a transmission line (often referred to as a channel), part of the signal will be reflected at the point of attachment(s). Reflections due to impedance mismatch ultimately causes problems with signal loss and tracking errors (jitter).
Prior attempts to control conductor spacing has been entirely for the purposes of stabilizing capacitance within a cable. It is well known in the industry that utilizing a cable with uniform capacitance between its pairs has the advantage of reducing crosstalk. U.S. Pat. No. 3,102,160 explains how equal and uniform capacitance can be achieved along a transmission line by simultaneously extruding dielectric over two conductors.
However, U.S. Pat. No. 3,102,160 did not recognize problems encountered with impedance mismatch at high frequencies. The impedance of the cable was of little importance provided the capacitance of each pair within the cable was relatively uniform. The problem is in that different cables can have uniform capacitances between their respective pairs and yet possess different average impedances.
Another problem with the U.S. Pat. No. 3,102,160 is with regard to insulated conductor separation. In order for the pairs of the said cable to be used with current LAN systems and connecting hardware, the adjoined insulated conductors must have the ability to be separated from one another for at least 1 inch along the length of the pair. The prior art provides no means for the separation of the two adjoined insulated conductors.